Plans for a 31km subsea road tunnel are unfrozen again in Japan.

Tunnel is proposed between Japan's main island of Honshu with Hokkaido island in north.  There is already a tunnel between these islands. Seikan tunnel. But it is a railway tunnel. If plans become real, the new road tunnel will cost 720 billion yen ($6.97 billion) excluding tunnel portals and connecting roads.

https://asia.nikkei.com/Business/Engineering-Construction/7bn-plan-for-new-Japan-undersea-tunnel-warms-up-after-years-on-ice